Dresden 2011 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 11: Precision spectroscopy of atoms and ions III

A 11.5: Vortrag

Dienstag, 15. März 2011, 15:00–15:15, BAR 205

The Size of the Proton from Muonic Hydrogen — •Tobias Nebel and for the CREMA-collaboration — Max–Planck–Institut für Quantenoptik, Garching, Germany.

The charge radius R_p of the proton has so far been known with a precision of about 1% from both electron scattering and precision spectroscopy of hydrogen.

We have recently determined R_p by means of laser spectroscopy of the exotic "muonic hydrogen" atom [1]. Here, the muon, which is the 200 times heavier cousin of the electron, orbits the proton with a 200 times smaller Bohr radius. This enhances the sensitivity to the proton’s finite size tremendously.

Our new value R_p = 0.84184 (67) fm is ten times more precise than the generally accepted CODATA value, but it differs by 5 standard deviations from it. A lively discussion about possible solutions to the "proton size puzzle" has started.

[1] R. Pohl et al., "The size of the proton", Nature 466, 213 (July 2010)